Contemporary computer and communications systems commonly comprise several subsystems, each implementing one or more computation or communication functions. Each subsystem is outfitted with external connector sockets for communicating with other subsystems and for drawing power. The subsystems are mounted in proximity to each other in mechanical structures in the form of industry standard sized racks or custom-sized chassis.
FIG. 1A illustrates a representative contemporary computing center having two servers 1 and a data storage 2. The servers 1 include subsystems 3 that are housed in industry-standard 19-inch racks. The subsystems 4 of the storage 2 are housed in a custom-size chassis. The servers 1 and storage 2 are typically in an environmentally controlled data center or server room. The subsystems 3-4 are interconnected with each other and to outside communication links through electronic or optical cables 5. AC or DC electrical power must also be supplied to the subsystems 3-4 and is typically distributed via under floor cabling 6 from a power source.
The rack/chassis-based architecture of FIG. 1A has several advantages: (1) the subsystems may be arbitrarily arranged in the room, subject to cooling and cabling distance constraints, and (2) the subsystems may have different form factors. However, this type of packaging suffers from several operational disadvantages: (1) scaling difficulty; (2) cable management; (3) connector unreliability; and (4) unreliability of wire and cable assemblies. These problems contribute to the overall unreliability of today's high-performance computer and communications systems and lead to increased costs of ownership, maintenance, and upgrade of the systems.
The first disadvantage of current computer and communications systems is the difficulty one would encounter when the system's capacity or functions need to be expanded. This can occur even if a system was designed to accommodate a certain degree of growth. For example, to connect a new server into a network, additional communication cables need to be connected to a network switch. However, if the switch is fully allocated at capacity with insufficient free network ports, the upgrade becomes difficult and costly, particularly if the system must remain operational while the expansion is performed.
The second disadvantage of current computer and communications systems is the management of interconnect cabling and wiring. Given the large number of wires and cables in a computer facility, it is not uncommon that service and support personnel may incorrectly connect or disconnect a cable. The potential for other errors, such as plugging a cable into a wrong subsystem and leaving a cable unconnected, can also occur, particularly when system operation must be restored quickly. For optical cables, one must select the proper speed, wavelength, and distance parameters.
The third disadvantage of current computer and communications systems is the unreliability of connectors. Electrical connectors can degrade over time due to micro-fretting wear, which can lead to corrosion. As a metal connector corrodes, its electrical resistance increases, causing intermittent or hard failures in the system. Optical connectors may be mishandled, jarred, or contaminated by finger oil or dust, causing an intermittent open circuit in the system. In addition, optical-to-electrical transceivers can fail. These hazards and failures result in an increased cost of maintenance for the system.
The fourth disadvantage of current computer systems is the unreliability and cost of cables. Both electrical and optical cables can be broken, cracked, bent, compressed, or otherwise mishandled. Glass-based optical cables can also be damaged if stepped on or if the maximum bending radius is exceeded. Although cables are typically designed to meet certain system parameters, they are not always manufactured to such tolerances.
Electrical cables may also carry undesirable shield or ground currents between subsystems with chassis grounds or signal grounds at different electrical potentials, particularly when the subsystems are powered from different AC branch circuits. Cables can also undesirably pick up external electromagnetic interference or electrostatic discharges. These unwanted shield, ground, or signal currents can cause intermittent or hard errors in the communication between the subsystems, resulting in transient or hard failures in the whole systems.
The above disadvantages contribute to the unreliability, inflexibility, and high cost of ownership of existing computer and communications systems. Therefore, there remains a need for a modular computer system that has reliable and simple interconnection, and is easy to expand and service. To address this need, a scalable computer system has been previously disclosed in U.S. patent application Ser. No. 10/264,893, which uses upon surface-mounted capacitive couplers for intercommunication. These couplers can be made from a variety of materials with different advantages. Rigid couplers, such as ceramic, have the advantage of being commercially available and easily integrated into a package by nature of the strength of the material. Being thick and self supporting they can be easily mounted mechanically and easily soldered for electrical connection.
Conversely, thin, flexible, polymer-type couplers, such as Kapton, Upilex, Teflon, etc, have different advantages. Technically, thin flexible couplers are advantages primarily due to the fact that their flexible nature eliminates the variable of substrate flatness. When substrates are not flat, the gap that is created between the halves of the coupler are not only large, but variable, which will limit the speed of data transfer. The flexibility of the flexible couplers allow them to be assembled in such a way as to have the couplers in intimate contact, such that only a dielectric layer over the metal coupler pad defines the separation.
Available flexible dielectric substrates, such as Kapton, also have the advantage of improved signal characteristics. The lower intrinsic dielectric constant of these materials reduces interfering cross-talk between adjacent channels.
Flexible couplers have the advantage of reduced manufacturing costs. Where rigid couplers, such as ceramic, have high materials costs and machining costs, flexible organic material is inexpensive and can be bulk processed. It also can be quickly and easily laser machined.
Finally, although rigid couplers are durable for mounting and soldering, they are brittle and therefore fragile. Rigid couplers such as ceramic will shatter on impact or if twisted. Flexible organic dielectrics are extremely durable to shocks or twisting. They are also able to withstand high temperatures and are chemically resistant.
The advantages of thin flexible couplers make them outperform the rigid interposers. However, integration of these couplers relies on the ability to make connection to the back side of the coupler via soldering. In the case of existing rigid couplers, such as ceramic, this is not an issue. However, in the case of a flexible dielectric materials (e.g. Kapton, Teflon, Upilex, etc), soldering to the backside of the coupler impairs the function of the coupler. Soldering a wire to the back side of a thin flexible material has a variety of challenges associated with it. Due to the thin cross-section of these dielectric films, and their poor thermal conductivity, the localized heating associated with soldering results in local hot spots which heavily taxes materials characteristics, such as adhesion of metals. Even more important than this is the form taken by the solidified solder, and the resulting deformation of the dielectric. Due mostly to the rigidity of the wire being connected to the coupler, the front surface of the coupler is most likely going to be deformed during soldering as shown in FIG. 1B. In FIG 1B, the dielectric film 7 is deformed along with the bonding pad 8 when the wire 9 is soldered to the pad using solder 10.
Even if the deformation of the front surface can be overcome such that the front surface of the coupler is not significantly compromised by the soldering operation, there are still several problems associated with direct soldering of wires to the coupler. Connecting multiple wires to the small area provided by the coupler can present similar problems that the existing system includes meaning cable management and unreliability of wire and manual solder connections. These wires can also limit the freedom of motion of the coupler, limiting the proximity of the coupler to the matching coupler. Finally, individual soldering of each wire will drive up cost, compounded by the additional cost it would require to overcome these technical challenges listed.
There is a need in the art for a flexible capacitive coupler assembly for providing for communications between computer subsystems.